全文获取类型
收费全文 | 9332篇 |
免费 | 1771篇 |
国内免费 | 1882篇 |
专业分类
化学 | 6847篇 |
晶体学 | 229篇 |
力学 | 652篇 |
综合类 | 144篇 |
数学 | 967篇 |
物理学 | 4146篇 |
出版年
2024年 | 27篇 |
2023年 | 129篇 |
2022年 | 312篇 |
2021年 | 388篇 |
2020年 | 439篇 |
2019年 | 385篇 |
2018年 | 362篇 |
2017年 | 392篇 |
2016年 | 461篇 |
2015年 | 534篇 |
2014年 | 657篇 |
2013年 | 816篇 |
2012年 | 790篇 |
2011年 | 857篇 |
2010年 | 730篇 |
2009年 | 658篇 |
2008年 | 770篇 |
2007年 | 702篇 |
2006年 | 635篇 |
2005年 | 527篇 |
2004年 | 401篇 |
2003年 | 310篇 |
2002年 | 321篇 |
2001年 | 297篇 |
2000年 | 226篇 |
1999年 | 170篇 |
1998年 | 106篇 |
1997年 | 103篇 |
1996年 | 99篇 |
1995年 | 64篇 |
1994年 | 44篇 |
1993年 | 48篇 |
1992年 | 31篇 |
1991年 | 26篇 |
1990年 | 30篇 |
1989年 | 22篇 |
1988年 | 15篇 |
1987年 | 21篇 |
1986年 | 14篇 |
1985年 | 16篇 |
1984年 | 13篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1971年 | 3篇 |
1959年 | 2篇 |
1957年 | 2篇 |
1948年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
81.
通过对左手材料的理论分析,设计了一种宽频带左手材料结构单元.该结构单元由一个矩形闭合环和十字型结构构成的谐振器和金属线组合而成.这种新结构中的谐振器实现负磁导率,金属线实现负介电常量,经过合理的设计,可以在某一频段内使得磁导率和介电常量同时为负,即具有负的有效折射率和正的波阻抗.数值仿真结果表明:在其工作频段内存在一个通带并且在17.6~29.0GHz频率范围内折射率实部为负,而虚部接近于零;同时在该频率范围内波阻抗实部大于零,从而说明了该左手材料具有左手特性.除此之外,相对左手带宽达到48.9%,远远优于传统的左手材料. 相似文献
82.
In order to increase the ability of ultrasound to penetrate high-attenuation medium,an attenuation matching method of ultrasonic Barker-coded excitation is prop... 相似文献
83.
Eu2+,Dy3+共掺杂硼铝锶长余辉玻璃陶瓷 总被引:13,自引:0,他引:13
首次介绍了一种新型长余辉材料:Eu^2 ,Dy^3 共掺杂硼铝锶长余辉玻璃陶瓷,该玻璃陶瓷用紫外灯、日光、荧光灯均可激发,发射黄绿色余辉,余辉的发射峰位于516nm,来自于Eu^2 的5d→^8S7/2跃迁。用12000 lx的荧光灯激发样品20分钟,停止激发后10秒时,该玻璃陶瓷的余辉亮度为3.53cd/m^2,色坐标为:x=0.2842,y=0.5772;停止激发后5小时55分钟,该玻璃陶瓷的余辉亮度为0.01cd/m^2;停止激发30小时后,余辉在黑暗中仍肉眼可见。文中对该玻璃陶瓷的相关性质进行了表征,并提出了可能的长余辉机理。 相似文献
84.
By analyzing the radiation dose on PIN photodetectors in space radiation environment, the variation of photocurrent and dark current after radiation is obtained. On the basis, the bit error rate of satellite laser communication based on space radiation dose of PIN photodetectors is established. According to simulation, when radiation dose is about 1.6 × 103 Gy and 7 × 104 Gy, bit error rate reaches 10−6 induced by 50 MeV and 10 MeV protons separately; and when radiation dose is within the range of 5 × 10 Gy–6 × 105 Gy, electrons and gamma-ray irradiation also cause increase in bit error rate to 10−6. The principle of damage dose on bit error rate is investigated, and the influence of decision threshold on bit error rate is further discussed. The result shows that when radiation dose is 1 MGy, if decision threshold is increased from 4.3 × 10−7 A to 5.5 × 10−7 A, bit error rate will decrease about 4 orders of magnitude. Hence, a proper decision threshold can improve system bit error rate efficiently. 相似文献
85.
Development of Two‐Channel Phosphorescent Core–Shell Nanoprobe for Ratiometric and Time‐Resolved Luminescence Imaging of Intracellular Oxygen Levels 下载免费PDF全文
86.
The charged Dirac oscillator on a noncommutative plane coupling to a uniform perpendicular magnetic field is studied in this paper. We map the noncommutative plane to a commutative one by means of Bopp shift and study this problem on the commutative plane. We find that this model can be mapped onto a quantum optics model which contains Anti-Jaynes-Cummings (AJC) or Jaynes-Cummings (JC) interactions when a dimensionless parameter ζ (which is the function of the intensity of the magnetic field) takes values in different regimes. Furthermore, this model behaves as experiencing a chirality quantum phase transition when the dimensionless parameter ζ approaches the critical point. Several evidences of the chirality quantum phase transition are presented. We also study the non-relativistic limit of this model and find that a similar chirality quantum phase transition takes place in its non-relativistic limit. 相似文献
87.
Zhihang Peng Dongxu Yan Qiang Chen Deqiong Xin Dan Liu Dingquan Xiao Jianguo Zhu 《Current Applied Physics》2014,14(12):1861-1866
Aurivillius phase Bi3Ti1−xTaxNb1−xWxO12 high temperature piezoceramics were prepared by a conventional solid state reaction method. The crystal structure, dielectric, electrical conduction and piezoelectric properties were systematically studied. Pure or modified Bi3TiNbO9 ceramics revealed the presence of only two-layered Aurivillius phase, indicating that Ta/W doping entered into the B-site of pseudo-perovskite structure and formed solid solutions. The Curie temperature had a strong reliance on the structural distortion. Furthermore, Ta/W dopants act as a donor doping, decrease the number of oxygen vacancies and facilitate the domain wall motion. As a result, Ta/W modifications significantly increase the DC resistivity and piezoelectric properties. Bi3Ti0.98Ta0.02Nb0.98W0.02O12 ceramics possess the optimum d33 value (∼12.5 pC/N) together with a high TC point (∼893 °C). Moreover, the resonance–antiresonance spectra demonstrate that the Ta/W-BTN ceramics are indeed piezoelectric in nature at 600 °C. The d33 value of BTTNW-2 ceramic remains ∼12.2 pC/N after annealing at 700 °C. These factors suggest that the BTTNW-based ceramic is a promising candidate for ultra-high temperature sensor applications. 相似文献
88.
Nonlinear spin excitations in ferromagnetic spin chains are studied for spintronic and magnetic devices including magnetic‐field sensors and for high‐density data storage. Here, (2+1)‐dimensional nonlinear Schrödinger equation is investigated, which describes the nonlinear spin dynamics for a Heisenberg ferromagnetic spin chain. Lie point symmetry generators and Lie symmetry groups of that equation are derived. Lie symmetry groups are related to the time, space, scale, rotation transformations, and Galilean boosts of that equation. Certain solutions, which are associated with the known solutions, are constructed. Based on the Lie symmetry generators, the reduced systems of such an equation are obtained. Based on the polynomial expansion and through one of the reduced systems, group‐invariant solutions are constructed. Soliton‐type group‐invariant solutions are graphically investigated and effects of the magnetic coupling coefficients, that is, α1, α2, α3, and α4, on the soliton's amplitude, width, and velocity are discussed. It is seen that α1, α2, α3, and α4 have no influence on the soliton's amplitude, but can affect the soliton's velocity and width. Lax pair and conservation laws of such an equation are derived. 相似文献
89.
Creation of Entanglement with Nonlocal Operations 总被引:5,自引:0,他引:5
ZHANG Yong CAO Wan-Cang LONG Gui-Lu 《理论物理通讯》2005,44(4):625-630
We discuss how to create more entanglement with nonlocal operations acting on two-particle states. For a given nonlocal operation, we find that some input states cannot produce entanglement and some produce the maximal entanglement, and find that any initial entangled states can produce more entanglement than initial product states. 相似文献
90.
We consider solving eigenvalue problems or model reduction problems for a quadratic matrix polynomial Iλ2 − Aλ − B with large and sparse A and B. We propose new Arnoldi and Lanczos type processes which operate on the same space as A and B live and construct projections of A and B to produce a quadratic matrix polynomial with the coefficient matrices of much smaller size, which is used to approximate the original problem. We shall apply the new processes to solve eigenvalue problems and model reductions of a second order linear input-output system and discuss convergence properties. Our new processes are also extendable to cover a general matrix polynomial of any degree. 相似文献